This application relates to and claims priority to corresponding Germany Patent Application No. 101 56 884.3, which was filed on Nov. 20, 2001, and which is incorporated by reference herein.
1. Field of the Invention
The invention relates to a securing arrangement for a mount of an optical element, in particular in a lens systems for semiconductor lithography, on a component, the mount being mounted, by at least three bearing bodies in corresponding bearing locations of the component, and the mount and the component being held together via magnetic forces.
2. Description of the Related Art
Reproducible interfaces or arrangements for retaining optical elements which can be exchanged in a reproducible manner, and in the case of which statically determined mounting is used, are known from practice, use being made, inter alia, of the following principles: xe2x80x9cthree balls-three V-groovesxe2x80x9d, xe2x80x9cthree balls-six cylindersxe2x80x9d or xe2x80x9cthree balls-cone-groove-planexe2x80x9d. These statically determined mountings allow one element to be accommodated in the other element in a reproducible manner. In stationary applications, in the simplest scenario, it is possible to use the weight of the part which is to be mounted in order to ensure the contact of the contact surfaces. If this is not possible in design terms, for example since installation has to take place from beneath, or if it is possible for relatively high forces which are not oriented in the same direction as the weight (e.g. during transportation or as a result of dynamic excitation) to occur, then an additional exterior retaining force which prevents the contact surfaces from being raised is necessary. It is usually the case that screw, clamping or spring connections and the like are used for this purpose. It is also possible to use magnets which connect the mount to the higher-level system, e.g. a housing of a lens system in semiconductor lithography.
It is usually the case, however, that moments are transmitted to the mount of the optical element by the design-induced position of the force-producing elements or by production tolerances, at the force-introduction locations. These moments then, in certain circumstances, result in disadvantageous deformation, both of the mount and of the optical element connected to it.
Moreover, there is also considerable outlay if the connection has to be released. It is also then the case that the reproducibility of the latter is no longer ensured with the necessary precision since, when the connection is joined together again, the optical element may be subjected to other types of moments which adversely effect the imaging quality thereof.
For the specific purpose of using the arrangement for securing the optical element as an end plate for a lens system in semiconductor lithography, reference should be made to EP 0 724 199 B1 and U.S. Pat. No. 5,973,863. These disclose different applications which are likewise concerned with exchangeable end plates. The two documents bring to light the problem that such plates, if they have to be exchangeable, should allow for the necessity of very precise positioning and of very straightforward and quick exchange.
The object of the present invention is thus to provide an arrangement for retaining an optical element, of the type mentioned in the introduction, which can be exchanged in a reproducible manner and has a retaining force which differs from the weight and is intended for fixing the elements without the optical element being subjected to deformation.
This object is achieved by an arrangement wherein the magnetic flux in said component is obstructed in the region of the bearing locations by a section of relatively low permeability, whereby the magnetic flux via said bearing bodies, made of magnetically highly permeable material, upon connection of said mount and component can be short-circuited by at least one magnet.
These features make it possible, in a straightforward and advantageous manner, for the mount and component to be connected firmly by the bearing bodies of the mount being introduced into the bearing locations of the component and being held together firmly by the magnetic field produced by short-circuiting. It is also advantageous that it is possible to dispense with screw, clamping or spring connections during the production.
A particularly advantageous development of the invention is that the bearing locations and the bearing bodies are designed such that merely normal forces occur between the bearing locations and the bearing bodies.
Since merely normal forces occur between the bearing locations and the bearing bodies upon connection of the mount and component, global deformation of the interface parts is advantageously avoided. Accordingly, the mount of the optical element is not subjected, at the force-introduction locations, to any disruptive moments which could result in deformation of the mount and thus of the optical element.
According to the invention, it may further be provided that the component is formed from three magnetically conducting segments which are separated by the bearing locations, a material with a considerably lower magnetic permeability being provided in the region of the bearing locations than elsewhere in the segments.
These features easily make it possible for a magnetic flux to run from a magnetic north pole via the first segment, via the first bearing body introduced into the first bearing location, to the second segment, via the second bearing body introduced into the second bearing location, to the third segment and, from there, via the third bearing body introduced into the third bearing location, to the magnetic south pole.
By virtue of the resulting magnetic flux, the bearing bodies are connected firmly to the bearing locations by magnetic forces.
It is advantageous if at least one of the segments has a separation, a material of low magnetic permeability being introduced into the resulting interspace, and it being possible, by means of said material, for a magnetic field to be coupled in by the magnet which bridges the separation.
It is thus easily possible for the bearing bodies to be connected, firmly to the bearing locations by virtue of the magnetic field being coupled in, and they can be raised off from one another in a force-free manner by virtue of the magnetic field being coupled out. Installation expediently takes place here with the magnetic field coupled out. It is only when the defined position of the mount in the component has been reached that the magnetic field is coupled in.
In one configuration, it may further be provided that the separation has an opening for accommodating the magnet.
This feature easily makes it possible to introduce a magnet into the component, it being possible for the magnetic field to be coupled in or switched by said magnet.
In a development of the invention, it may be provided that the poles of the magnet can be adjusted mechanically in relation to the separation of adjacent segments such that the magnetic field can be switched, and that the magnet is designed as a cylindrical permanent magnet.
These features make it possible for the magnetic field to be easily switched on and off manually or mechanically by virtue of the poles being adjusted. A cylindrical permanent magnet may be introduced into a cylindrical opening and can be adjusted by straightforward rotation.
It is advantageous if the magnet is designed as a solenoid.
This embodiment makes it possible for the magnetic field to be switched electrically without being subjected to mechanical or manual action.
Alternatively, it is also possible for the magnet to be designed as a permanent magnet which can be switched off by an electric counter-magnet.
According to the invention, it may further be provided that the bearing locations and the bearing bodies each have a hard surface at least in the contact regions.
These features additionally avoid deformation in the contact regions and ensure that normal forces act at the force-introduction locations.
It is advantageous if the bearing locations have grooves.
With the grooves it is possible for the bearing bodies to be introduced in a straightforward and advantageous manner into the groove-containing bearing locations.
According to the invention, it may further be provided that the grooves each have a V-shape.
The V-shape serves to provide normal forces in the case of, for example, spherical bearing bodies being mounted in the V-shaped grooves of the bearing location. The V-shape of the grooves results in a geometrically optimized arrangement of the magnetic lines of force in this region.
It is advantageous if the hard surface of the bearing locations are formed by hard-metal rollers or by hard-metal plates or by virtue of being nickel plated or hard-chrome plated.
By virtue of these embodiments, it is straightforwardly possible, in production terms, to provide a large number of different kinds of bearing locations with hard surfaces to avoid deformation, depending on requirements.
In a development of the invention, it may be provided that the bearing bodies are of spherical design at least in the region of the contact surfaces, and that the bearing bodies are designed as balls or rollers.
These features make it possible, for example in combination with a V-shaped design of the grooves of the bearing locations, to ensure that normal forces act particularly precisely at the force-introduction locations of the bearing locations and bearing bodies, and thus to prevent deformation of the carrying element and of the optical element. The normal forces each act only at a point, in the case of a spherical bearing body, or only on a straight line, in the case of a roller-like bearing body.
Exemplary embodiments of the invention are illustrated in principle hereinbelow with reference to the drawing, in which: